Question

I’m seeing a strange behavior in my code, here’s an analogous example using apples and persons, but the code is basically the same:

List<Apple> apples = ...
var selectableApples = apples.Select(a => new SelectableApple { SelectedByPerson = null, Apple = a });

foreach (Person person in persons)
{
    foreach (var unselectedApple in selectableApples.Where(aa => aa.SelectedByPerson == null))
    {
        if (/*the person satisfies some conditions*/)
        {
            // This gets executed like 100 times:
            unselectedApple.SelectedByPerson = person;
        }
    }
}

foreach (var selectedApple in selectableApples.Where(aa => aa.SelectedByPerson != null))
{
    Unreachable code - the collection is empty... WTF???
}

The SelectableApple class is just a plain C# class without logic, and public getters and setters for all the properties.

Why does this happen?

Thanks in advance!

Answer 1

The selectedApples is not a collection that contains objects, it’s an expression that creates a collection on the fly. That means that the changes that you do to the objects are discarded, and when you loop selectedApples again it will be recreated from scratch.

Make it a collection using the ToList method:

var selectableApples = apples.Select(a => new SelectableApple { SelectedByPerson = null, Apple = a }).ToList();